黄芩素在人及不同种属肝微粒体中的UDP-glucuronosyltransferase代谢差异（摘要）

目的：研究黄芩素在不同种属肝微粒体中的UDP-葡萄糖醛酸转移酶（UDP-glucuronosyltransferase, UDPGA）代谢差异特性。方法使用肝微粒体体外代谢孵育法、HPLC-UV分析方法，选用不同种属的肝微粒体进行黄芩素UDPGA体外代谢研究。结果黄芩素在人肝微粒体及不同种属的肝微粒中，加入UDPGA进行37℃恒温孵育，孵育结束后离心，取上清液，经HPLC-UV分离检测得到3个代谢产物，分别是：黄芩素-7-O-β-葡萄糖醛酸结合物、黄芩素-6-O-β-葡萄糖醛酸结合物和黄芩素-6-O-葡萄糖醛酸结合物-7-O-β-葡萄糖醛酸结合物；通过与标准品对照确定黄芩素的三个代谢产物都是葡萄糖醛酸化的代谢产物。同时，不同种属间UGT代谢物的活性表现出较大差异，黄芩素-7-O-β-葡萄糖醛酸结合物在人肝微粒体中的代谢活性最强，Km=1.61，Vmax=0.77（BG在人肝微粒体中的代谢活性是SD雌鼠的25.2倍）；黄芩素-6-O-β-葡萄糖醛酸结合物在比格犬肝微粒体中代谢活性最强，Km=3.05，Vmax=3.51（雄性比格犬肝微粒体的活性是雄性恒河猴肝微粒体的2.6倍）；黄芩素-6-O-葡萄糖醛酸-7-O-β-葡萄糖醛酸结合物在猪肝微粒体中代谢活性最强，Km=5.38， Vmax=0.17（猪肝微粒体的活性是人肝微粒体的13.6倍），其他依次是犬、恒河猴、鼠和人。结论黄芩素在人及不同种属肝微粒体UGT代谢中均生成上述三种葡萄糖醛酸化代谢产物，但是不同种属间的代谢表现出酶动力学的差异。

Species and Gender Differences Affect the Metabolism of Baicalein via Glucuronidation

Baicalein （5, 6, 7-trihydroxyflavone） is one of the typical representatives of flavonoids, which is isolated from Scutel-laria baicalensis Georgi, and has been demonstrated to possess a variety of biological activities, including anti-inflammation, cardiovascular protection, etc. Recently, accumulating evidences have demonstrated the antitumor activity of this flavone in a variety of human cancer cell lines in vitro. Though it has so many pharmacological effects, its species diversity remains unclear. The aim of this study is to define the mechanisms responsible for poor bioavailability of Baicalein by its metabolism using in vitro of liver. Liver microsomes of Rhesus monkeys, SD rats, Beagle dogs, pigs and humans, among which Rhesus monkeys, SD rats and Beagle dogs using gender comparison, were employed to phase II metabolic incubation system. Origin 8.0 software was used for analysis of kinetic data and evidenced by a liner Eadie-Hofstee plot. Our experiment reveals that there are three glucuronidation metabolites of Baicalein incubated with human liver microsomes, monkey liver microsomes, SD rats （F/M） liver microsomes, dog （F/M） liver microsomes and pig microsomes at 37℃for 30min and determined by using of HPLC-UV. Through the analysis of kinetic data, Km values of Baicalein-7-glucuronidation in human liver microsomes （Km=1.74） are about 25-fold lower than in female SD rats （Km=43.8）. The metabolite Baicalein-6-glucuronidation is catalyzed by liver microsomes, which is an active metabolite with 16-fold higher affinity to the SD rats （Km=0.56） than Rhesus monkeys （Km=9.39）. The other metabolite, Baicalein-6-O-glucuronidation-7-O-glucuronidation, in native hepatic microsomes from female SD rats （Km=156） liver displayed higher Km values than that in pigs （Km=6.48）. In human liver microsomes, metabolites of Ba, BG’and BGG, Km values are 3.93 and 88.4, respectively. Results suggest that we should not select single animal model to conduct animal experiment. Besides, our data also show that there are great differences in gender in some species, BG, BG’and BGG in SD rats and BG in dogs have remarkable differences. The species and gender metabolic differences we observed between animals and human liver provide key informa-tion for delineating Baicalein pharmacokinetics needed for human health risk assessment. In conclusion, species and gender affect Baicalein metabolism to a different degree, and experimental animals are expected to be useful to predict the Baicalein glucuronidation in humans.